Conventionally, Al—Sn base, Al—Sn—Si base, Al—Zn base materials are known as a slide alloy made of an aluminum-base alloy, for example, an aluminum-base bearing alloy for internal combustion engines. The aluminum-base bearing alloy is generally bonded to a steel back metal through an intermediate layer made of pure aluminum or an aluminum-base alloy and is manufactured as bearings.
In order to cope with a high output power in recent internal combustion engines, ones having an excellent fatigue resistance and a high strength have been developed among such aluminum-base bearing alloys. Since soft materials exhibit a favorable bonding property, however, pure aluminum or aluminum-base bearing alloys having a low hardness have been used as an intermediate layer. However, when a high load is acted on that intermediate layer, for which pure aluminum or aluminum-base bearing alloys having a low hardness are used, plastic deformation is caused due to softness thereof and the intermediate layer is squeezed out from bearing end surfaces.
In order to solve the problem, there has been proposed an aluminum-base alloy bearing, in which an intermediate layer has a Vickers hardness that is 40% or more but 70% or less of the hardness of an aluminum-base bearing alloy, the intermediate layer has a Vickers hardness of 25 or more, and the aluminum-base bearing alloy has a Vickers hardness of 50 or more (JP-B2-2564012).
Intermediate layers having a low hardness have been used in order to improve the bonding property of an aluminum-base bearing alloy for a steel back metal. When an aluminum-base bearing alloy having a high hardness is used in order to cope with a high output power of engines, an intermediate layer having a hardness that amounts to 40% or more of the hardness of the aluminum-base bearing alloy is satisfactory in terms of fatigue resistance but is too hard and poor in bonding property.